Femoral Cartilage Ultrasound Echo‐Intensity Is a Valid Measure Of Cartilage Composition

ABSTRACT This study aimed to create a conversion equation that accurately predicts cartilage magnetic resonance imaging (MRI) T2 relaxation times using ultrasound echo‐intensity and common participant demographics. We recruited 15 participants with a primary anterior cruciate ligament reconstruction between the ages of 18‐35 years at 1‐5 years after surgery. A single investigator completed a transverse suprapatellar scan with the ACLR limb in max knee flexion to image the femoral trochlea cartilage. A single reader manually segmented the femoral cartilage cross‐sectional area to assess the echo‐intensity (i.e., mean grey‐scale pixel value). At a separate visit, a T2 mapping sequence with the MRI beam set to an oblique angle was used to image the femoral trochlea cartilage. A single reader manually segmented the cartilage cross‐sectional area on a single MRI slice to assess the T2 relaxation time. A stepwise, multiple linear regression was used to predict T2 relaxation time from cartilage echo‐intensity and common demographic variables. We created a conversion equation using the regression betas and then used an ICC and Bland‐Altman plot to assess agreement between the estimated and true T2 relaxation time. Cartilage ultrasound echo‐intensity and age significantly predicted T2 relaxation time (F=7.33, p=0.008, R 2 =0.55). When using the new conversion equation to estimate T2 relaxation time from cartilage echo‐intensity and age, there was strong agreement between the estimated and true T2 relaxation time (ICC 2,k =0.84). This study provides promising preliminary data that cartilage echo‐intensity combined with age can be used as a clinically accessible tool for evaluating cartilage composition. This article is protected by copyright. All rights reserved.